METHOD OF PRODUCING HIGH-STRENGTH STEEL SHEET WITH COATING, HAVING HIGH STRENGTH, DUCTILITY AND MOLDABILITY Russian patent published in 2019 - IPC C21D9/46 C21D9/48 C21D1/18 C21D8/02 C22C38/38 C22C38/02 C23C2/00 

FIELD: iron metallurgy.

SUBSTANCE: present invention relates to a method of producing a high-strength coated steel sheet having a YS yield strength of at least 800 MPa, ultimate strength TS of at least 1180 MPa, full elongation of at least 14 % and HER orifice distribution coefficient of at least 30 %, as well as to high-strength steel sheet with coating produced by the proposed method. Method consists in heat treatment and application of coating on sheet steel and includes following stages: sheet heating to annealing temperature TA, which is more than Ac3, but below 1000 °C, and holding the sheet at said annealing temperature TA for time of 30 to 300 s, sheet cooling to QT temperature of 250–350 °C with cooling rate sufficient to obtain structure immediately after cooling from martensite and austenite, wherein content of martensite is at least 60 %, and content of austenite is such that final structure contains from 3 to 15 % of residual austenite and from 85 to 97 % of martensite and bainite without ferrite, holding sheet at cooling temperature QT during holding time from 2 to 8 s, heating sheet to temperature redistribution PT 430–480 °C and holding sheet at this temperature during time of redistribution Pt 10–90 s. At that, the chemical composition of steel contains in weight percent: 0.15 % ≤ C ≤ 0.25 %, 1.2 % ≤ Si ≤ 1.8 %, 2 % ≤ Mn ≤ 2.4 %, 0.1 % ≤ Cr ≤ 0.25 %, Al ≤ 0.5 %, with rest presented by Fe and unavoidable impurities.

EFFECT: present invention relates to a method for producing a high strength coated steel sheet having improved strength, ductility and formability and to the sheets obtained with the method.

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